A key component of a conventional thermal dye transfer printer is the thermal printhead. In many thermal printers, the thermal printhead has a ceramic substrate side and a circuit board side bonded together to an aluminum backer plate. The ceramic substrate side has a plurality of heating elements (heater line) for transferring dye from a ribbon onto paper. The circuit board has integrated circuits laterally spaced from the ceramic substrate on the bottom and connectors on the top to supply power and data for selectively operating the heating elements. In some printers, the integrated circuit is enclosed in a protective housing that has two walls and a cover between the walls, with one wall distal from the ceramic substrate and transverse to the substrate and the other wall proximate to the ceramic substrate and varying in height from a minimal level proximate the level of the substrate to a maximum level of the cover. Alternatively, in other printers the integrated circuit is covered by a junction coated resin to protect the integrated circuit.
In a conventional thermal printer, a receiver medium 12, such as a paper, fabric, film, or other web or sheet type material, is clamped between a capstan roller and a pinch roller and pulled through a nip between the thermal printhead and the platen. The capstan and pinch rollers are driven by a stepper motor that provides both precise movement and control of the paper sheet. The printhead and platen capture a web of donor material with dye and press it against the paper. In some printers the platen spins freely while the web and receiver are pulled past the printhead and in other printers the platen is driven. Heat from the thermal head transfers dye from the donor web onto the receiver medium to create an image.
Using this process, thermal dye transfer printers create continuous tones of specific colors not unlike those of traditional color photo prints. Whereas traditional color photos use dyes and fine grains of silver salts, chemically processed to produce an image, thermal printers achieve continuous tones by laying their cyan, yellow and magenta dyes on top of each other with repeated passes of the paper past the printhead. (Some thermal printers also add black dye to the final process). Thermal dye transfer printers also have the capacity to use their heat provided by the printhead to seal a clear plastic layer over the completed print giving the final product an estimated 100-year lifespan.
An example of a conventional thermal dye transfer printer that provides monotone, multi-tone or full color printing is shown in FIG. 1. Conventional printer 10 has a sheet of receiver medium 12 that is driven along a print path 14 by capstan roller 16 and pinch roller 18. A printhead 20 is opposite a free spinning platen 22. Donor supply roller 24 and donor take up roller 26 support a web 28 of thermal dye donor material. A bias spring 30 presses printhead 20 against donor web 28 that contacts receiver medium 12. A pinch spring 32 urges pinch roller 18 against capstan roller 16. Capstan roller 16 is turned by a stepper motor 34. A belt 36 connects the capstan roller 16 to stepper motor 34. A leading edge of the receiver medium 12 is fed through a feed nip 38 between capstan roller 16 and pinch roller 18 so that receiver medium 12 and donor web 28 are pulled past the printhead 20 and platen 22 where donor material is transferred to receiver medium 12.
As illustrated, conventional printer 10 has printhead 20 normally positioned with an integrated circuit cover 40 extending into the plane of the print path. As such, receiver medium 12 must be turned to bend beneath integrated circuit cover 40. Whenever receiver medium 12 is deflected from a straight path and must be curved or bent to travel along a bent path, there is a higher likelihood that receiver medium 12 will be diverted from the precise alignment required of a receiver medium 12 during thermal printing. This can cause variations in registration that can create unwanted image artifacts. Thus, what is needed is a thermal printer having more easily established registration.